1. Field
The present invention is related to processors, and, more particularly, to dynamic power control of low power processors.
2. Background Information
Achieving significant power savings in embedded processors, such as microprocessors, for example, and other digital systems is becoming increasingly desirable. One reason is the increase in the use of cell phones and other hand-held portable devices having limited battery capacity. In addition, the computing power of such hand-held devices is increasing as the technology evolves, and will continue to increase for the foreseeable future. This is particularly likely with the addition of digital signal processing and communications capability to such devices and systems, as well as software applications, such as voice recognition, which will predictably utilize and potentially drive this increasing computational demand.
In systems that employ such processors, it is not unusual for the battery voltage to tend to be higher than a particular voltage level employed for successful operation and, therefore, voltages provided by the battery are often stepped down, such as via a voltage regulator. Another reason a higher voltage may be provided is that modern high frequency silicon fabrication processes for processors, such as microprocessors, tend to tolerate lower voltages than the processes employed to fabricate other components. Therefore, typically the regulators provide multiple output levels of voltage for different components of the system. Furthermore, as the batteries wear out, typically the voltage output level drifts downward and, therefore, voltage regulators are also employed in this context to provide a substantially consistent operating voltage over the battery life. Recently, more complex regulators that provide the capability to switch between step down and step up operation have become available and may be useful in this environment. Such a regulator steps the battery voltage down when the battery is relatively new or recharged, and steps the voltage up when that voltage has degraded over time to a level which is insufficient to proper operation of the system, thereby extending the useful battery lifetime.
As is well known, power consumption is related to the voltage level of the voltage supply by the following equation: P=C(Vdd)2F, where F is the operating frequency, C is the switched capacitance, and Vdd is the power supply voltage. As this equation demonstrates, power may be significantly reduced by lowering the voltage level of the supply voltage. Unfortunately, the maximum performance obtainable for a given operating frequency F is also related to the supply voltage as follows: Id(sat)=xcex2(Vddxe2x88x92Vt)xcex1, where Id(sat) is the drain current at saturation, Vdd is the drain-to-source voltage, and Vt is the threshold voltage. xcex1 is a process dependent parameter and is typically taken to be 2, but may be between one and two and xcex2 has its usual meaning, well known in the art, including the width and length parameters for an metal-oxide semiconductor (MOS) transistor. Consequently, because systems are designed to operate at a voltage level that meets their peak computational performance demands, they consume significant amounts of power which is not useful at times when the peak computational capability is not required. In such systems, power is typically saved by xe2x80x9cclock gating.xe2x80x9d In this approach, the sections of the device or system which are unused have the clocks that drive those sections turned xe2x80x9coff.xe2x80x9d This lowers the effective frequency of operation, resulting in a linear improvement, as indicated by the equation above, essentially by lowering the average frequency by including zero frequency time spans into the average. A need, therefore, exists for a technique that improves the reduction in power consumption for these low power devices, while still delivering sufficient computational performance to complete the tasks desired.
Briefly, in accordance with one embodiment of the invention, a system includes: a processor, a voltage regulator, and a memory. The voltage regulator is coupled to the processor to adjust the operating voltage of the processor. The memory is coupled to the processor by a memory bus. The memory has stored on it processor instructions that, when executed by the processor, result in modification of the operating frequency of the processor and result in adjustment of the operating voltage of the processor, based, at least in part, on dynamic changes in the processing load of the processor.